Auto-focusing optical system

ABSTRACT

An automatic focusing optical system having a range determining system and a photo-taking system. The photo-taking system is divided into two groups with a beam splitter interposed therebetween. The range determining system has its forward group provided by the whole or part of the forward group of the phototaking system and has its rearward group disposed in the path of light reflected by the beam splitter. All or part of the rearward group of the photo-taking system is axially moved for focusing the photo-taking system.

United Stat1- Nakamura 1 1 Sept. 4, 1973 [54] AUTO-FOCUSING OPTICALSYSTEM 3,232,197 2/1966 Kasahara 350 202 ux 2,503,789 4/1950 Wood etal.......... 350/255 [75] lnvenm" 5mm Kamakum'kem 3,612,663 10/1971Tronnier et a1 350 214 Japan [73] Assign: 2255: u Chlyoda-ku PrimaryExaminer-John K. Corbin Attorney-Joseph M. Fitzpatrick.John Thomas Cella [22] Filed: Mar. 31, 1972 r l 211 Appl. No.: 240,213

[57] ABSTRACT [30] Foreign Apphc'mn Pnomy Data An automatic focusingoptical system having a range Apr. 16, 1971 Japan 46/23900 determiningsystem and a photmmking system The photo-taking system is divided intotwo groups with a [52] US. Cl 350/202, 95/42, 350/172, beam splitterinterposed therebctweem The range 350/214 termining system has itsforward group provided by the [51 Int. Cl. G02b 9/64, G02b 27/10 who: orpan f the f d group f the photmmking [58] Field of Search 350/202, 214,171 system d h it r arward group disposed in the path 350/172; 95/42 oflight reflected by the beam splitter. All or part of the rearward groupof the photo-taking system is axially [56] Rekrences cued moved forfocusing the photo-taking system.

UNITED STATES PATENTS 3,385,190 5/1968 8110 et a] 95/42 3 Claims, 8Drawing Figures r|r2 3F4rs rer7lsr PAIENIEUSEP 4m:

SHEEI 1 [F 3 vamama oagmc wcmc wcsoc Pmmsnxr'qn 3.756.691

SNEEI 3 0F 3 FIG. 3

ABERRATIONS OF RANGE DETERMINING LENS igggffig SINE CONDITION BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates to anoptical system for the socalled self-focusing camera in which aphotoelectric element is moved back and forth to find a position wherethe image of a range determining optical system is sharpest, whereafteran electric logic circuit and an analog circuit are used to calculatethe amount of axial movement to be imparted to a photo-taking lens inaccordance with said position and the current position of thephoto-taking lens so that a servo-motor is driven in accordance with theresult of the calculation to automatically move the photo-taking lensfor efiecting the focusing.

2. Description of the Prior Art In constructing the optical system forthe camera of the described type, there comes to mind a twin-lens camerahaving a photo-taking lens system constructed in parallel relationshipwith respect to a range finder system.

In such a twin-lens camera, the presence of the two entirely discretelens systems leads to an increased size of the entire camera structureand, in addition, the parallax occurring between the photo-taking lensand the range finder lens necessitates the provision of a correctionmechanism.

The problem of parallax mibht be avoided by constructing the camera as asingle-lens reflex type. However, if the type is used in which a beamsplitter is disposed in front of the photo-taking lens, the beamsplitter must have a large diameter in order to prevent the oblique rayspassing through the photo-taking lens from being turned down. Reductionin the size of the beam splitter might be reailized by incorporating itin the interior of the photo-taking lens system. This, however, presentsa problem in that thebeam splitter is moved together with thephoto-taking lens when the latter is axially moved for focusing, andthus complicates its operative association with the range determiningsystem. Also, in the triplet type lens or in a zoom lens, which involvesaxial movement of the foremost lens element, the interlocking mechanismfor the range determining system will still be complicated and, thus,impractical.

SUMMARY OF THE INVENTION In order to overcome the problems encounteredwith the prior art, the present invention provides a phototaking lenssystem which is divided into forward and rearward groups, with a beamsplitter interposed therebetween. The focusing of the photo-taking lensis achieved by axially moving all or part of the rearward group thereof.v

This leads to compactness of the beam splitter which is mounted adjacentthe diaphragm, and accordingly, reduces the dimensions of the opticalsystem, even if use is made of a semi-transparent mirror or prism, or ofa hollow mirror having a transparent center portion.

On the other hand, the entire system is simplified because the focusingof the photo-taking lens is achieved by axially moving only the rearwardgroup of the photo-taking lens system mounted independently of therearward group of the range determining system. Moreand this, in turn,leads to the compactness of the optical system and, accordingly, of theentire camera.

It will thus be appreciated that the present invention provides acompact self-focusing camera.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will become fullyunderstood from the following description of an embodiment thereof takenin conjunction with the accompanying drawings, in which:

FIG. 1 is a side elevational view showing the construction according toone embodiment of the present invention;

FIGS. 2a to 2f show a series of graphs'illustrating various aberrationswhich occur when the object distance from the photo-taking lens in theembodiment of FIG. 1 is at infinity and at 1.5 m, respectively; and

FIG. 3 is a graph showing the spherical aberration and sine conditionwhen the object distance from the range finder system in the embodimentof FIG. I is at infinity.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the embodiment ofthe present invention shown in FIG. 1, the photo-taking lens systemcomprises a forward group designated by r, to r, inclusive, and arearward group designated by r to r inclusive. The range finder systemis provided by part of the forward group, i.e., r to r,. A beam splitter10, which is in the form of a hollow mirror, is interposed between theforward and the rearward group of the photo-taking lens system so as toreflect object light downwardly to a group of lens elements disposedbelow the beam splitter to focus the image of the object therethrough.

Range finding is achieved by moving part of the rearward group such as rto r axially forward in the systerm The data of the embodiment is shownin the table below, wherein r,, r, r, represents the radii of curvatureof the sucessive lens elements, 4,, d, d,, the center thicknesses or theintervertex air spaces of the successive lens elements, in, n, n. therefractive indices of the respective glass materials for d-line, and11,, v, v, the Abbe numbers of the respective glass materials.

Various aberrations are shown in FIG. 2, which occur when the objectdistance from the photo-taking lens in the illustrated embodiment of thepresent invention is infinite and 1.5m. Curves M and S in theastigmatism graphs represent meridional beam and sagittal beam,respectively. Spherical aberrations and sine conditions for the infiniteobject distance from the range finder system are illustrated in FIG. 3.

EXAMPLE Photo-taking Lens: Focal length f mm, relative aperture F/4.5,for use with a still camera;

Range Finder Lens; Focal length f 50mm, relative aperture F/0.8

(r,r are common to the photo-taking lens and the range finder lens) I.An automatic focusing optical system comprising a main photo-takingoptical system formed to be an inverted telephoto lens, consisting of afront divergent lens group including at least one positive member and atleast one negative member, the diameter of said positive member beinglarger than that of said negative member, and a first rear convergentlens group axially movable for focusing the image of the object; and afocused range determining optical system for formingthe object image ona photoresponsive element including a second rear convergent lens grouplocated in front of the photoresponsive element and an aperturedinclined mirror placed between said front divergent lens group and saidfirst rear convergent lens group for directing a part of the light raysfrom the object to the optical axis of said second convergent lensgroup, 1

whereby the light rays from the object, passing through the negativemember of the front divergent lens group and the aperture of saidmirror, are focused by said first rear convergent lens group. and

the light rays from the object, passing through the peripheral portionof said positive member outside of said negative member are reflected bythe reflecting surface of said mirror toward said second convergent lensgroup.

2. An automatic focusing optical system according to claim 1, whereinsaid first rear group includes a stop and three convergent components,the first component thereof being positioned between said mirror andsaid stop, 7

thereby the remaining second and third positive components of said threecomponents are axially moved in unison for focusing.

3. An automatic focusing optical system according to claim 2, wherein:

a photo-taking lens is characterized by:

A photo-taking lens is characterized by:

a focal length f= mm, relative aperture F/4.5, for

use with a still camera;

and a range finder lens is characterized by:

a focal length f 50mm, relative aperture F/0.8; r to r,, inclusive arecommon to the photo-taking lens and'the range finder lens,

wherein:

rP-SGZJ fla -3.2 Iv -1.80482 A -46.

rp -H104 Abbe numbers of the respective glass materials.

* i l i 3 U D STATES PATENT OFFICE CERTIFICATE OF CORRECTI 'Parenr No.3,756,697 Dated September 4. 1973- Inventor) SOICHI NAKAMURA It iscertified that error appears in theabove-identified patentand that saidLetters Patent are hereby corrected as shown below:

Column 1, line 29, change "mibht" to might line 36, change "reailized"to realized Column 4, line 23, delete "A' photo-taking lens ischaracterized by:"-; line 35, change "r 42.672" to r =42.672 line 36,change '"n =l.5l6l8 to Signed and sealed this 9th day of April 197b,.

(SEAL) g I Attest: v v v a.

EDWARD ILFIETCHERJR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents Column 3,line 23, change i-1595.00" tor =l595.00

FORM PO-IOSO (10-69) USCOMM DC 603766369 s 0.5. Govnnuem nuurms ornc:19" o-su-au

1. An automatic focusing optical system comprising a main phototakingoptical system formed to be an inverted telephoto lens, consisting of afront divergent lens group including at least one positive member and atleast one negative member, the diameter of said positive member beinglarger than that of said negative member, and a first rear convergentlens group axially movable for focusing the image of the object; and afocused range determining optical system for forming the object image ona photoresponsive element including a second rear convergent lens grouplocated in front of the photoresponsive element and an aperturedinclined mirror placed between said front divergent lens group and saidfirst rear convergent lens group for directing a part of the light raysfrom the object to the optical axis of said second convergent lensgroup, whereby the light rays from the object, passing through thenegative member of the front divergent lens group and the aperture ofsaid mirror, are focused by said first rear convergent lens group, andthe light rays from the object, passing through the peripheral portionof said positive member outside of said negative member are reflected bythe reflecting surface of said mirror toward said second convergent lensgroup.
 2. An automatic focusing optical system according to claim 1,wherein said first rear group includes a sTop and three convergentcomponents, the first component thereof being positioned between saidmirror and said stop, thereby the remaining second and third positivecomponents of said three components are axially moved in unison forfocusing.
 3. An automatic focusing optical system according to claim 2,wherein: a photo-taking lens is characterized by: A photo-taking lens ischaracterized by: a focal length f 80mm, relative aperture F/4.5, foruse with a still camera; wherein: r1 174.94 d1 7.5 n1 1.62299 Nu 1 58.1r2 -362.34 d2 0.1 r3 135.09 d3 13.5 n2 1.60311 Nu 2 60.7 r4 -104.02 d42.0 n3 1.75520 Nu 3 27.5 r5 10000.00 d5 3.7 n4 1.69895 Nu 4 30.0 r6<42.672 d6 1.0 n5 1.51618 Nu 5 64.2 r7 50.88 d7 4.4 r8 -43.756 d8 1.2 n61.62041 Nu 6 60.3 r9 142.270 d9 39.538 r10 121.42 d10 4.0 n7 1.62041 Nu7 60.3 r11 -48.713 d11 1.0 n8 1.62004 Nu 8 36.3 r12 -148.14 d12 10.877r13 80.803 d13 4.7 n9 1.54814 Nu 9 45.9 r14 -1347.294 d14 0.7 r15 32.37d15 10.4 n10 1.53172 Nu 10 48.9 r16 -209.947 d16 2.8 n11 1.7847 Nu 1126.1 r17 44.615 d17 38.1 r18 137.03 d18 3.8 n12 1.62041 Nu 12 60.3 r19-71.03 d19 3.0 r20 -31.35 d20 1.5 n13 1.744 Nu 13 44.9 r21 40.00 d21 4.9n14 1.69895 Nu 14 30.0 r22 -1595.00 d22 0.1 r23 62.328 d23 4.0 n151.70154 Nu 15 41.1 r24 2466.00 and a range finder lens is characterizedby: a focal length f 50mm, relative aperture F/0.8; r1 to r5 inclusiveare common to the photo-taking lens and the range finder lens, wherein:r1 174.94 d1 7.5 n1 1.62299 Nu 1 58.1 r2 -362.34 d2 0.1 r3 135.09 d313.5 n2 1.60311 Nu 2 60.7 r4 -104.02 d4 2.0 n3 1.75520 Nu 3 27.5 r510000.00 dp5 67.0 rp6 -28.00 dp6 1.0 n4 1.68893 Nu 4 31.1 rp7 60.00 dp78.0 n5 1.691 Nu 5 54.8 rp8 -28.989 dp8 0.1 rp9 22.00 dp9 4.0 n6 1.74443Nu 6 49.4 rp10 25.287 dp10 0.1 rp11 10.25 dp11 3.2 n7 1.80482 Nu 7 46.4rp12 12.104 where r1, r2. . . rn represent the radii of curvature of thesuccessive lens elements, d1, d2. . . dn 1 the center thicknesses or theintervertex air spaces of the successive lens elements, n1, n2. . . nkthe refractive indices of the respective glass materials for d-line, andNu 1, Nu 2 . . . Nu k the Abbe numbers of the respective glassmaterials.